1. Field of the Invention
The present invention relates to an image pickup apparatus with auto focus function which can be used for a digital camera, and an auto focus method.
2. Description of the Related Art
Currently, in the digital camera, a contrast type having no focus detection dedicated element structure is mainly used as the auto focus system.
In the contrast type of the auto focus system, the focus is detected based on the contrast of the image captured by CCD (Charge Coupled Device) which is of the image pickup device, and a point (focus lens position) where a value of the contrast of the image becomes the maximum is set at a focusing point.
Accordingly, in order to obtain the focusing point, it is necessary that contrast data is obtained at each distance by moving a focus lens to perform a drive scanning in an AF search range from the shortest distance to infinity. However, when the drive scanning is performed in the AF search range from the shortest distance to the infinity, there is a problem that a long time is required for the focusing operation (namely, the number of switching steps of a stepper motor moving the focus lens is increased).
Therefore, in some conventional digital cameras, a focusing range from the shortest distance to the infinity is previously divided into a close photograph movement range and a normal photograph movement range. When an operator selects one of photograph modes (macro photograph mode for close photograph and normal photograph mode for normal photograph), the focus lens is first moved within a movement range corresponding to the selected photograph mode. When the focusing point cannot be detected within the movement range corresponding to the selected photograph mode, the focusing point is detected within the other movement range, thereby shortening the time required for an auto focus operation by moving the focus lens.
In another conventional image pickup apparatus, when an object position is located in a macro region (close photograph AF search range) in the normal photograph mode, or when the object position is located in a normal region (normal photograph AF search range) in the macro photograph mode, the operator is encouraged to perform switch to the proper photograph mode by a warning message, or the switch to the photograph mode is automatically performed.
Further, there is an automatic focusing technology including means for selecting one of the normal photograph mode and the macro photograph mode and means for determining whether or not the object can be focused in the AF search range of the selected mode. In the automatic focusing technology, when the means determined that the object cannot be focused, the AF search range of the other mode is specified to perform focusing control.